Well known automatic pool cleaners utilize a cleaner body coupled to a flexible conduit which supplies power to propel the body forwardly along a substantially random travel path though the pool. For example, U.S. Pat. Nos. 6,090,219 and 6,365,039 (reissued as RE 38,479) describe automatic pool cleaners which use a body powered by supplied positive pressure water for cleaning the interior surface of a pool containment wall and the upper surface of a water pool contained therein. Other U.S. patents describe cleaner bodies which are powered by a negative pressure water source and/or electric power. Regardless of the particular body configuration and power source a number of known cleaners include some type of timer mechanism for periodically initiating a timed “back-up” or “repositioning” operation to allow the body to escape form being trapped by an obstruction in the pool and/or enhance randomization of the body's travel path. Additionally, some available patent documents (e.g., U.S. Pat. No. 6,365,039; U.S. Pat. No. 6,398,878; PCT/US2004/016937) suggest the inclusion of a motion sensor for sensing when the rate of forward motion of the cleaner body diminishes below a certain threshold rate. This can occur, for example, when the body gets trapped by an obstruction. The sensed decrease in the rate of forward motion can be used to initiate the repositioning operation to free the body.
Aforementioned U.S. Pat. No. 6,398,878 describes an automatic swimming pool cleaner which includes a propulsion subsystem for producing a force FP for propelling a cleaner body in a forward direction, a motion sensor for reporting when the body's rate of forward motion is less than a certain threshold rate, and a repositioning subsystem for producing a force FR for redirecting the body's forward motion along a different travel path. The preferred repositioning subsystem described in said '678 patent redirects the body by applying the force FR (FIGS. 1A, 1B) in a direction to translate the body rearwardly and rotate it around an axis oriented substantially perpendicular to the direction of the body's forward motion. Aforementioned International application PCT/US2004/016937 describes an enhanced propulsion subsystem.
Although the application of the repositioning force FR as described in said '878 patent is generally effective to free a cleaner body trapped by an obstruction, it has been observed that excessive body rotation can contribute to the formation of tangles, e.g., persistent coils and/or knots, in the conduit supplying power to the body. The formation of such tangles is undesirable because tangles tend to impede the free travel of the body and increase the time dedicated to repositioning at the expense of the time available for cleaning. It has also been observed that tangles are more likely to occur when a timed repositioning operation is initiated while the body is transitioning between a travel path at the wall surface. (i.e., wall surface mode) and a travel path at the water surface (i.e., water surface mode).